What is it

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What is it?
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Faults

• Homework due today -
• New homework assignment handout today

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Joints Geometry planar plumose structure
joint sets Kinematics walls move apart very
slightly in direction of pull Mechanics form
by tensile loading cooling removal of
overlying rock Other abundant in uppermost crust
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Under compression, rocks fail along shear
fractures (sliding motion rather than pulling
apart motion)
Introduction to Faults (p. 269-279 286-296)
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Fault Shear fractures along which there is
visible offset generally planar or curviplanar
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Strike-slip faults Accommodate horizontal slip
between adjacent blocks steep (vertical) faults
left lateral (sinistral)
right lateral (dextral)
left lateral vs. right lateral sense-of-slip
relative to a chosen block
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What is it? left lateral vs. right lateral
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For faults that are not vertical.
Hanging wall The block above the
fault. Footwall The block below the fault.
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Normal fault hanging wall moves down with
respect to footwall
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What is it?
Normal faults generally place younger and/or
lower-grade rocks (in HW) on top of older and/or
higher-grade rocks (in FW)
HW
young low-grade dirt
FW
old high-grade gneiss
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Normal faults generally place younger and/or
lower-grade rocks (in HW) on top of older and/or
higher-grade rocks (in FW)
What is it?
Cambrian limestone
FW
HW
Tertiary conglomerate
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Thrust fault (reverse fault) hanging wall moves
upward relative to footwall
What is it?
HW
FW
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Thrust faults generally place older and/or
higher-grade rocks (in HW) on top of younger
and/or lower-grade rocks (in FW)
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Thrust faults generally place older and/or
higher-grade rocks (in HW) on top of younger
and/or lower-grade rocks (in FW)
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Thrust faults generally place older and/or
higher-grade rocks (in HW) on top of younger
and/or lower-grade rocks (in FW)
What is it?
HW
sandstone
low grade
blueschist
FW
high grade
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• Normal faults accommodate lengthening

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• Thrust faults accommodate shortening

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http//earth.leeds.ac.uk/learnstructure/index.htm
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Slip vs. Separation Slip ACTUAL relative
displacement Separation APPARENT relative
displacement
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A natural example demonstrating that apparent
separation can be much different than true slip!
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• The key to describing slip along a fault lies in
  measuring
• (1) Direction of displacement
• (2) Sense of displacement
• (3) Magnitude of displacement

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Listric curved faults that flatten with depth
listric normal fault
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• Map Symbols a start
• Strike-slip fault
• Normal fault
• Thrust fault

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Next lecture Intro to folds Read pgs. 372-413
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Announcements Field trip to Cottonwood
Canyon this Saturday - meet at 745 am at the
loading dock! Bring pencils, protractor Will it
rain? Rain gear Will it be hot? Sunscreen lotion
Hiking boots, water, lunches Will be back
around 4 pm.